1. Field of the Invention
This invention relates to a control valve, more particularly to an improved control valve which is to be connected to a water tank for automatically controlling the supply of water into the water tank without electricity in order to maintain a predetermined minimum water level in the water tank.
2. Description of Related Art
Referring to FIG. 1, a water heater (W) has a first water tank (21) for receiving unboiled water and a second water tank (22) for heating unboiled water and supplying boiled water. The second water tank (22) has a heating element (23) mounted adjacent to a bottom thereof. A conduit (24) is connected to the first water tank (21) and the second water tank (23). A non-return valve (11) is mounted on the conduit (24) to control the flow direction of water from the first water tank (21) to the second water tank (22). A control valve (10) is mounted on the conduit (24) upstream from the non-return valve (11) to control the water transmission from the first water tank (21) to the second water tank (22). Generally, the control valve (10) is manually operated. The heating element (23) is overheated and is easily damaged when the water level in the second water tank (22) is below the level of the heating element (23) and water is not immediately transmitted from the first water tank (21) to the second water tank (22) by actuating the control valve (10) manually. In addition, the control valve (10) may be an electromagnetic valve which operates automatically to provide water immediately from the first water tank (21) to the second water tank (22) when the water level in the second water tank (22) is below the level of the heating element (23). Therefore, the heating element (23) is not easily damaged and has a long service life. The one drawback is that electricity is necessary for the electromagnetic valve.